Human dermal microvascular endothelial cells (HDMEC) are strategically located to play an important role in the cutaneous inflammatory response. Because of the difficult in growing these cells in pure culture, little is known about their functions in inflammatory skin diseases. This laboratory has recently succeeded in isolating and culturing pure HDMEC from neonatal foreskins. These HDMEC can be expanded to large cell numbers and used in functional studies. In addition, this laboratory recently succeeded in inducing both human umbilical vein endothelial cells (HUVE) and HDMEC to undergo extremely rapid differentiation in vitro. The differentiated endothelial cells become elongated and form tubes with lumina that resemble microvessels in vivo. We will systematically study the role of microvascular endothelial cells in cutaneous inflammation and define the signals that induce endothelial cell differentiation. Studies in this proposal will characterize the immunologically relevant cell surface receptors and antigens, as well as cell adhesion molecules present on differentiated and undifferentiated HDMEC, in order to gain insights into the potential immunologic functions of these cells. The ability of biologic response modifiers to induce or modulate the expression of these molecules will be precisely defined. This proposal will assess the ability of purified human T-lymphocytes and monocytes to bind to undifferentiated and differentiated HDMEC and HUVE to delineate the mechanisms of leukocyte- endothelial cell interaction. The subpopulations of T-cells that bind will also be defined. In addition, the cell adhesion molecules responsible for T-cell and monocyte adherence to HDMEC will be defined using specific monoclonal antibodies directed against T-cell, monocyte, and endothelial cell adherence molecules. The ability of commonly used therapeutic modalities such as corticosteroids, and ultraviolet light to affect expression of cell adhesion molecules and cell-cell adherence will be systematically assessed. Related studies in this proposal will utilize cytotoxicity assays to assess the presence of antiendothelial cell antibodies in sera of patients with cutaneous and/or systemic vasculitis. The cell surface molecules bound by the antiendothelial cell antibodies will be immunoprecipitated and analyzed immunochemically. Thus, the studies in this proposal will provide new and important insights into the initiation and evolution of cutaneous inflammation and have direct bearing on the pathophysiology of inflammatory skin diseases.